Abstract [en]

A series of donor-acceptor substituted biphenyls is examined using semiempirical SCF-MO methods. The geometries, dipole moments and first hyperpolarizabilities are obtained from AM1, MNDO and PM3 calculations. The finite-field method is used to calculate the polarizabilities. The properties of the substituents and the torsion angle between the phenyl rings are of fundamental importance for the hyperpolarizabilities. Among the three methods, AM1 leads to torsion angles closest to the experimental data. For each molecule, the HOMO is found to be localized on the donor part to some extent, whereas the LUMO is more concentrated on the acceptor part. The spectroscopic properties of the molecules are investigated using the ZINDO model. For all the molecules considered, the transition from the HOMO to the LUMO is found to be the most important for charge transfer, and this transition has been used in a two-state model to compute the first hyperpolarizability.